Triptorelin acts by lowering the level of testosterone in the body. The testes will only make testosterone if told to do so by another hormone called luteinising hormone, which is produced by a part of the brain known as the pituitary gland. Triptorelin reduces the production of luteinising hormone, so the levels of testosterone fall. This may result in shrinkage or slowing down of the growth of the cancer. There may be a brief increase in testosterone levels in the first few days or weeks of starting tretment.